Gas turbine engines are known, and typically include a fan delivering air into a compressor. The air is compressed in the compressor, and delivered into a combustion section where it is mixed with fuel and ignited. Products of the combustion pass downstream over turbine rotors, which in turn drive the compressor and fan.
Fan rotors are becoming increasingly large in diameter. This increase presents challenges with regard to operation and packaging. Thus, it has been proposed to drive a plurality of fan rotors from a single gas turbine engine core. The enlargement of fan diameter has increased with the recent development of a gear reduction driving the fan from the turbine rotor. The fans typically drive air through both a bypass duct, and into the compressor. A bypass ratio is defined as the volume of air delivered into the bypass duct as propulsion, compared to the volume of air delivered into the compressor. The bypass ratio has become larger as the fan diameter has become larger.
It has been proposed to drive a plurality of smaller fan rotors from a single core engine. Typically these proposals have only driven two fan rotors. One proposal has been to drive as many as four fan rotors from a single core engine, however, the transmission for doing so would not share the power to the fan rotors in an efficient manner.